Wetland Mitigation 2

[MCD917]

How do you create a wetland? There is a site where we are required to do mitigation and it has to be of like-kind. Is it as simple as lowering the grade and planting like-kind plant species there? I searched several websites including the EPA and have been having a difficult time finding specific, cut and dry standards for creating wetlands. This particular site is in MD.

I would just like to know where I could go to find out this information. Thank you

 

[saruman26]

You're basically right on the mark - a shallow basin with wetland plants.

The Pennsylvania BMP Handbook (January 2005, Draft), Section 6.13 Constructed Wetlands provides details and construction information. The book can be obtained in PDF format at the following link:

http://www.dep.state.pa.us/dep/subject/advcoun/Stormwater/stormwatercomm.htm

Let us all know if you have any additional questions. Good luck!

 

[MCD917]

Thank you for the information. But, can these standards be applied to Maryland?

 

[saruman26]

Maryland? - even better. I used to work in Fairfax County, Virginia.

The design standards for Virginia, Maryland, and D.C. are very similar. Additionally, the Pennsylvania handbook is heavily based on the Virginina and Maryland BMP books.

http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/stormwater_design/index.asp.

This link is for the Maryland Stormwater Design Manual, which has sections for constructed wetlands.

 

[Hoagie]

Be careful MCD197....you may want to have a wetlands expert (biologist) lead the wetland's design. There are variables that aren't so obvious.....i.e. plant mortality, correct soils mixing/ammendments, reclaiming seed bed materials, etc. I usually ask the wetland's biologist to direct the grading. Wetlands mitigation sometimes requires a safety factor (sometimes as much as 4 times the disturbed/filled area)be used to account for failure in planting or pooling.

Good luck,

h.

 

[LHA]

While I would certainly invite the wetland's biologist to GIVE INPUT INTO the grading, I would not ask the wetland's biologist to DIRECT the grading.

The wetland's biologist end goal is to provide wetlands, yours is to maximize your client's land use. The design team's objective is to provide the best combination.

The law only requires replacement in-kind, so only replace in-kind. That means 0.1 acre remedial for 0.1 destroyed...no safety factor.

Women and cats will do as they please; men and dogs should just learn to live with that - Steve

 

[francesca]

Since nobody has mentioned it, I may as well add my 2c worth (which may be stating the obvious and may well be covered by those publications listed above).

You need to have hydrologic connectivity. It's no good having a pool if it only gets the water that lands on it.

Also, if you're obligated to do water quality, you can send your site runoff through the wetland and you're assured* of getting sufficient flow through the wetland to keep it wet and also your water is being treated by the vegetation.

*Well, only if your site is big enough.

 

[Hoagie]

Great tip Francesca...now that's worth reading.
H.

 

[mudhog]

What was your original question?Constructing a wetland or mitigating an existing wetland?They are two different animals.Are you mitigating the loss of the wetland type due to development?If so for who? COE can require from 1:1 up to 3:1 depending on type of wetland.There are several "types" of wetlands(shrub/scrub,shallow water,deep water,etc.etc)You need more site and biological/soil information.It takes 3 conditions to be present to meet the true COE 1987 Manual definition of "wetland".Hydric soils,hydrophytic vegetation,and hydrology.Hydroperiod and depth of flooding are the critical parameters for hydrology.Your consulting tree hugger and dirt dobber can handle the other two.
I agree that you need to work closely with the biologist.Be aware that someone(local authority,government agency,etc.)will have to sign off on your plan and wetland mitigation,wetland restoration,wetland enhancement,& wetland creation are dual discipline conservation practices.

You may want to check out C of Engineers and Natural Resources Conservation Service websites.You can start at these websites and then fineturn your search for your local state or district office.You are looking for practice codes and standards.
Hope I didn't complicate matters.It's not complicated,you just need to know who your audience is.

 

[bltseattle]

Wetland mitigation design usually employs several fields of expertise that have to coordinate to ensure a functional result. As an engineer, not a landscape designer or horticulturalist, you should not be put in a position where the decisions you make could result in poor plant survival. Replacing dead plants can be a major expense and it is important that the responsibility for that element lies with the landscape designer. The engineer's role in plant selection should be limited to providing the expected water surface elevations/hydrologic regime for the various growing seasons of interest to the landscape designer.

Based on my past experience, typical roles on the team are as follows (this is a quick brain-dump, these may or may not apply to your situation):

Permit coordination: often led by an environmental-type or the landscape architect, works with agencies to ensure the correct type of wetland is created and the right amount of that wetland is created. Relies on input from the rest of the project team to fill our permit info.

Landscape architect: develops concept/preliminary grading plan for use by civil; develops planting plan; specifies nature of soil improvement and subgrade preparation; responsible for planting & plant establishment procedures (specifications and plant establishment plan)

Civil engineer: provide hydrologic and hydraulic analysis/modeling; develop water budget for wetland to ensure proper seasonal water levels & volumes; provide the landscape designer with typical water levels for their use in delineating plant communities relative to the pond surface eleveation; assess need for pond liner (with input from geotech); design & detail pond liner; develop constructable grading plan for the plan set based on the LA's concept plan, including horizontal and vertical control points (how will it be staked?); detail for hydraulic features such as weirs or drop structures; ensure flotable habitat features (e.g. logs) are anchored (details); assess scour potential at inlet/outlet and address through design; provide quantities of cut/fill for permit purposes; develop erosion and sedimentation control plan; determine if/how to temporarily bypass existing flows during the construction.

Biologist: provide input to permit coordinator and landscape designer to ensure the biological/ecological design criteria are met; assist with plant selection; identify additional habitat features (logs, "snag" trees, etc.)

Geotechnical engineer: assess native soils and imported soils for seepage/infiltation potential; advise on pond liner need & options; provide bearing capacity under structures (e.g. weirs); advise on groundwater elevation relative to the proposed water surface elevations and implications thereof; advise on constructability.

I'm sure I forgot some items but the issues indicated above should at least be considered during the design process, and responsibilities assigned so that plants won't be mis-matched to the water regime, and the plan set is constructible. It's also good for the civil to provide some operational control of water amounts/routing, if possible, for example by providing an adjustable weir so water levels can be adjusted post-construction if needed.

Good luck!

 

[blueoak]

Just a comment on francesca's water quality comment.

Many states and the EPA often see wetlands as waters of the US or State and do not allow treatment within them. The new wetland would be considered this way since it should be comparable to the old wetland it is replacing. This is why you sometimes see wetland mitigations doubled even if not required, so you can claim treatment in the treatment portion and mitigation for the rest.

Otherwise, unless you have a park in the development you may want to just buy the necessary wetland credits from someone else, if allowed, and move forward. Most urban wetland mitigations are pretty useless for maintaining species diversity for both plants and animals so a large off site bank that is managed by a someone like the Nature Conservancy actually provides the "species" benefit of wetlands.

 

[zimballa]

I'm a grad student at Virginia Tech (Soil Science), with my research in wetland mitigation. One thing you need to make sure of is you don't just do the minimum for wetland creation. Several of the sites I have had experience in have failed to meet wetland status over the years. Just grading down land to the water table and planting some wetland species will greatly increase the chance for failure. Clients we have worked with, including VDOT (VA Department of Transportation) and DEQ have had sites where they chose to take the cheap way out, resulting in failure to meet COE requirements. The result is many years of work and millions of dollars, where if initial investments of choosing appropriate plants, installation of microtopographic features and strong attention to soil properties (bulk density, water holding, porosity, etc) can save money in the long run. I am not experienced in the engineering aspect of creation, but as mentioned in posts above, there is much more that needs to be considered. The dynamic aspect of wetlands requires several inputs from professionals of different fields (soil, hydrology, ecology, etc.).